The present invention relates generally to the manufacture of acetic acid and more particularly to a catalytic composition for use in a methanol carbonylation process including a homogeneous iridium catalyst system and a vinyl-pyridine polymer.
Polymers are known to be useful in catalytic systems used for carbonylating methanol to make acetic acid. Generally, polymers are suggested in the art as supports for catalysts. There is disclosed in U.S. Pat. No. 5,466,874 to Scates et al. a polymeric carbonylation catalyst system useful for the carbonylation of methanol to make acetic acid, acetic anhydride or both including a polymer support containing pendant pyrrolidone groups which support a rhodium species. See also U.S. Pat. No. 5,281,359 to Scates et al.
U.S. Pat. No. 5,334,755 to Yoneda et al. discloses a process for the production of acetic acid from methanol wherein the liquid system is contacted with a supported rhodium catalyst to produce acetic acid at a temperature from 140-250xc2x0 C. and a pressure of 15-60 kg/cm2G with a partial pressure of carbon monoxide of 7-30 kg/cm2 while maintaining (a) the water concentration of the solution in the range of 0.5-10% by weight and (b) the carbonylation degree Cxcex7 defined therein at 0.15 or more. The supported catalyst is prepared as described in Example 1, columns 9-10, wherein a cross-linked polyvinylpyridine/divinyl benzene copolymer resin is immersed in methanol with various catalysts components and the various components are heated to a relatively high temperature. The catalyst obtained is mixed into a reactant solution including methyl iodide, methanol and acetic acid after the solution is contacted with carbon monoxide in order to make acetic acid.
U.S. Pat. No. 5,364,963 to Minami et al. describes a rhodium catalyst supported on a vinyl pyridine resin useful for making acetic acid. The rhodium is supported on a cross-linked vinyl pyridine resin wherein the vinyl pyridine resin has a cross-link degree of 30-60%, a pore volume of 0.1-0.4 ml/g and an average pore diameter of 20-100 nm. The catalyst may be prepared by contacting the pyridine ring containing resin with an aqueous solution containing rhodium ion and then contacting the resulting rhodium ion carrying resin with carbon monoxide and an alkyl iodide in an organic solvent to convert the rhodium ion to a rhodium complex bound to the resin. Acetic acid is produced by reacting carbon monoxide with methanol at a temperature of 140-250xc2x0 C. and a partial pressure of carbon monoxide of 7-30kg/cm2 in the presence of an alkyl iodide. See also European Patent Publication No. 0567,331, Japanese Kokai No. 5-306254, Japanese Kokai No. 5-306253, as well as Japanese Kokai No. 6-285364.
U.S. Pat. No. 5,155,261 to Marston et al. discloses an improved Monsanto-type process for acetic acid preparation and a heterogenous supported catalyst for accomplishing the same. The method comprises reacting methanol with carbon monoxide under a pressure of about 65-80 Bar and temperature of 170-200xc2x0 C. in the presence of methyl iodide and a catalyst comprising an insoluble polymer having a pendant free base, N-oxide or quaternized pyridine groups supporting a rhodium species loaded to less than 10 weight percent (expressed as metal) of the polymer component.
Iridium has also been utilized as the primary catalytic metal component in homogeneous systems for the catalytic carbonylation of methanol to acetic acid. In European Patent Application Publication No. 0 849 248 there is disclosed a process for the production of acetic acid by carbonylating with carbon monoxide methanol and/or a reactive derivative thereof in a carbonylation reactor containing a liquid reaction composition including an iridium carbonylation catalyst, methyl iodide co-catalyst, a finite concentration of water, acetic acid, methyl acetate and at least one promotor wherein the water concentration is at or below that at which the maximum in the graph of carbonylation rate versus water concentration occurs and there is employed in the liquid reaction composition a co-promotor selected from the alkali metal iodides, alkaline earth metal iodides, metal complexes capable of generating I-, salts capable of generating I- and mixtures of two or more. It is noted on page 4 of the EPA ""248 publication that a co-promotor such as lithium should preferably be employed in the range of 0.5 to 1.5:1. That is, the molar ratio of the co-promotor to the iridium is in the range from 0.5:1 to 1.5:1. Polymers have also been reported as useful in these systems.
WIPO Publication WO 98/57918 discloses a process for the production of acetic acid utilizing a vinylpyridine supported Group VIII metal catalyst. In a typical embodiment, about 9 percent by weight of vinylpyridine is charged to a carbonylation reactor. See example 1, p. 10.
Various supports have been specifically suggested for supporting iridium catalyst. There is disclosed in U.S. Pat. No. 5,892,110 to Ramprasad et al. a process for producing acetic anhydride by the reaction of methyl acetate, carbon monoxide and hydrogen at elevated temperatures and pressures in the presence of an alkyl halide and a heterogenous bifunctional catalyst that contains an insoluble polymer having pendant quaternized phosphine groups some of which phosphine groups are ionically bonded to anionic Group VIII metal complexes, the remainder of the phosphine groups being bonded to iodide. The US ""110 patent reports than in contrast to earlier processes, no accelerator (promotor) is necessary to achieve the catalytic reaction and the products are easily separated from the catalyst by filtration. The catalyst can be recycled for consecutive runs without loss in activity. In general the catalysts include a polymer, such as a polymer with pendant phosphine groups and a Group VIII metal such as rhodium or iridium. See column 2, lines 55-60.
There is disclosed in WIPO Publication WO 98/33590 a supported catalyst including iridium and at least one second metal selected from the group consisting of ruthenium, molybdenum, tungsten, palladium, platinum and rhenium deposited on a support material. The preferred support materials are carbon, activated carbon, and silicone oxide sources. See page 6, lines 16-18. It should be noted that the WO ""590 publication does not disclose polymer supports.
U.S. Pat. No. 4,127,506 to Gray et al. discloses polymer supported catalyst prepared by photo-irradiation of low valent transition metal complexes such as CO2(CO)8, Rh4(CO)12 or RU3(CO)12 in the presence of solid polymers containing amine ligands such as polyvinylpyridine. Hydroformylation of all olefins to aldehydes at ambient temperatures is specifically disclosed. It should be noted that the US ""506 patent reports that the catalysts described therein are useful in a wide variety of reactions including hydrogenation, isomerization, hydroformylation, carbonylation, etc. (See column 3). Among the metals useful in polymer materials there are recited cobalt, nickel, iron, platinum, rhodium, palladium manganese, chromium, titanium, ruthenium, tantalum and iridium. See column 4, lines 15 to 20. The polymer typically contains amine ligands capable of coordinating with the low valent transition metals, preferably tertiary amines such as pyridyl and the like. Among the polymers specifically named are polyvinylpyridine, polyethylene imine, and polyvinylbenzimidazole.
There is disclosed in European Patent Application Publication No. 0 752 406 a process for the production of acetic acid by carbonylation. According to this EPA ""406 publication a carbonylation is carried out in the liquid phase in the presence of an iridium carbonylation catalyst, a methyl iodide co-catalyst and a promotor. The beneficial effect of the promotor is enhanced by continuously maintaining the liquid reaction composition no greater than 6.5% by weight water, 1 to 35% by weight methyl acetate and 4 to 20% by weight methyl iodide. It is noted in EPA ""406 publication, page 4, lines 28 et seq, and following that, in the iridium system, ionic contaminants such as corrosion metals, phosphines or nitrogen containing compounds or ligands which may quaternize in situ should be kept to a minimum in the reaction composition in order to avoid adverse effects on the reaction by generating Ixe2x88x92.
In the foregoing references, the amount of polymer employed is quite high in order to anchor the catalyst metal. It has been found, that contrary to the teachings of the prior art, relatively small amounts of a pyridine polymer is advantageous in a homogeneous, iridium catalyzed system.
It has been unexpectedly, and indeed surprisingly, found that the addition of relatively small amounts of a pyridine polymer to a homogeneous iridium catalyst system enhances the carbonylation rate in the manufacture of acetic acid. Relatively small amounts of perhaps as low as 0.01% or even lower and up to about 2 weight percent or perhaps more depending on the system appear to be effective. The homogeneous iridium system is well known and may include various promoters and co-promoters as further described herein. In typical commercial carbonylation processes, methanol and carbon monoxide are utilized as feedstocks.
The present invention thus provides in one aspect for enhanced, iridium-catalyzed carbonylation of methanol and/or its reactive derivatives by way of providing a catalytic composition including: (a) from about 100-6000 ppm iridium; (b) from about 1-70% methyl acetate; (c) from about 1-50% methyl iodide; (d) from about 0.1-15% water and (e) and insoluble pyridine ring containing polymer; wherein the weight ratio of the insoluble pyridine ring containing polymer to iridium is less than about 10.
Typically, the weight ratio of the insoluble ring containing polymer to iridium is less than about 5, with less than about 3 being preferred in some embodiments, whereas the weight ratio of the polymer to iridium is typically at least about 0.1 and preferably at least about 0.5.
Methyl iodide is typically present in the reactor between from about 1 to about 50 weight percent, with from about 2 to about 35 weight percent being more typical. Iridium is preferably present from about 1000 ppm to about 4,000 ppm.
Water should be present in the reaction mixture in at least a finite amount with from about 0.1 to about 15 weight percent being typical and from about 1 to about 10 weight percent being preferred.
Methyl acetate may be present in the catalytic composition in any suitable amount; typically from about 2 to about 50 weight percent, with from about 3 to about 35 weight percent methyl acetate in the reactor being more typical.
A suitable promotor may also be employed if so desired. Typical promoters include osmium compounds and ruthenium compounds as further described herein.
In preferred aspects of the invention, less than about 20 percent of the iridium in the catalytic mixture is anchored on the iridium, wherein from about 0.1 to 1 or up to about 10 percent or less of the iridium being anchored is typically preferred. Thus if a catalytic mixture contains about 4000 ppm iridium, preferably less than about 400 ppm is anchored to the polymer.
Unless otherwise indicated, percent or xe2x80x9c%xe2x80x9d as used herein refers to weight percent of the reactor mixture and ppm refers to parts per million by weight of the reactor mixture.